Various techniques for effective communication and resource utilization methods have been developed to maximize efficiency of limited radio resources for broadband wireless communication systems. One of the systems under consideration as the next generation wireless communication system is multiple carrier system. A multiple carrier system refers to the system which provides broad band services by collecting one or more carriers with smaller bandwidth than the bandwidth aimed by a wireless communication system providing the broadband services.
Although a wireless communication system such as the conventional 3GPP (3rd Generation Partnership Project) LTE (Long Term Evolution) employs carriers having various bandwidth, it is basically a system consisting of one carrier, namely, a single carrier system. Meanwhile, the next generation wireless communication system such as the LTE-A (Advanced) may correspond to a multiple carrier system using aggregation of multiple carriers, namely, carrier aggregation (CA). In a multiple carrier system, the carrier which forms the unit of carrier aggregation is called a component carrier (CC). In the multiple carrier system, a user equipment (UE) may be configured to have a plurality of downlink component carrier (DL CC) and a plurality of uplink component carrier (UL CC). In case for the UE receiving a plurality of transmission blocks through a plurality of DL CCs, the UE provides feedback of ACK/NACK (acknowledgement/negative acknowledgement) indicating whether each transmission block has been successfully received or demodulated. Therefore, the amount of transmitted information of ACK/NACK is increased compared with single carrier systems.
In order to transmit the increased ACK/NACK feedback, a new PUCCH (Physical Uplink Control Channel) format is under development and at the same time, a method of using a plurality of PUCCH resources is being taken into consideration. However, in case channel conditions are not favorable in the uplink, transmission of increased ACK/NACK information may become difficult due to limitations to transmission power.
Since the PUCCH structure specified for the 3GPP LTE system is designed based on two bits of ACK/NACK signal, there is needed a design for a control channel for carrying ACK/NACK signal with increased bit size.
Also, it should be noted that transmission blocks are not necessarily transmitted by a large amount of quantity at all times. Therefore, if the control channel is designed according to a maximum capacity, the resulting control channel might be rather inefficient for transmission of ACK/NACK signals with small bit size.
In this regard, there is a need for an efficient method and apparatus for transmitting uplink control information in a multiple carrier system.